42 M/Y Build - Questions

Discussion in 'Boatbuilding' started by Scarab, Sep 6, 2014.

  1. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    If I was faced with owning a boat such as that I'd make it a marina queen with limited propulsion, say with a "bolt on" pod fairing at the transom to smooth out some flow, counter the bouyancy of such with water tankage & with integrated twin outboard mounts for around 40-60hp a side to a large boarding platform...... most of this style of vessel in my area sit at the marina 99.9% of the time & on occassion go out to a nearby beach at 4 knots or so being limited by low wash zones...... as for blasting at 20-30-40 knots it gets exxy.
    Therefore I'd get nearly equal functionality, increased tankage etc. with a nice gen set, all the comforts of home & be as cool as all get out on my streamlined sports cruiser wearing me gucci sunglassess & spiffy docksiders & linen suit........... sippin on me cool beverage......
    Of course I'd leave provision to fit the big engines & running gear at a later stage.


    Jeff.
     
  2. waikikin
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    waikikin Senior Member

    Make it shiny & weather proof first, leave accessability through cockpit to saloon area cos there's lots of stuff/ply/soles/bulkheads to get in.

    Jeff.
     
  3. rustybarge
    Joined: Oct 2013
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    Location: Ireland

    rustybarge Cheetah 25' Powercat.

    Here's some fuel consumption figures for the Swift trawler 44'. (42' without swim platform/12 tons/twin 300hp)

    http://www.trawlerforum.com/forums/s3/sf-la-our-beneteau-swift-trawler-44-a-16200-4.html
    Quote: Hey Lost Horizons I did some calculating for you while we were out on the bay this weekend. Water was pretty flat and the tide was at the end of the slack and starting to flood (we were going against it). Here is the consumption for each engine and the speed. Your mileage may vary


    2 GPH at 8.5
    5 GPH at 10
    7 GPH at 13
    9 GPH at 16
    10 GPH at 18

    Remember to multiply by two for twin engines.
     
  4. Scarab
    Joined: Sep 2014
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    Scarab Junior Member

    Honestly.......

    What part of this conversation didn't you people understand?

    Trolls indeed.

    I'll multiply your twin engines by zero.
     
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  5. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    HP = (TORQUE X RPM) / 5252

    The type of powerplant (steam, internal combustion, electric) has no effect on this relationship.

    What is powering the jet drives? Isn't this like trying to pick yourself up by your own bootstraps?

    1. Few cars are 42 feet long and weigh 12-15 tons.

    2. The cars which are this size and weight are usually semi-tractor trailer rigs equipped with diesel engines putting out about 400-600 HP.

    3. It takes a lot less power to drive a car at 60 MPH through air than to drive a boat, even a small one, at 40 knots through water. In case you haven't realized it, water is a lot denser than air.

    4. The power requirements for a vessel operating in displacement mode vary approximately as the cube of the speed of the vessel. Thus, if it takes 10 HP to move a vessel at 10 knots, it will take 80 HP to move the same vessel at 20 knots, 270 HP at 30 knots, and 640 HP at 40 knots. This relationship is a function of the resistance characteristics of the vessel and is not affected by the type of power plant used.

    5. Electric motors and generators are heavy and expensive, being made almost entirely of iron and copper. If you think a 300 HP diesel engine is expensive, try pricing a 300 HP electric motor. A typical electric motor in this power rating runs between $15K and $30K new and weighs about 3000 lbs.

    6. It has been said that a boat is a hole in the water into which one pours money. I have a feeling you are about to prove the validity of this observation again.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The simple difference between a car and a boat is rolling resistance verses continuously increasing frictional (and other) resistance. A car needs the gas pedal pretty good to get rolling, but not all of it and once at speed can back off the pedal a considerable amount. At highway speeds, you're just touching the pedal. This isn't the case with continuous duty cycle propulsion systems (regardless of type). A boat, air plane, jet and other "devices" require a continuous amount of power applied. There's no backing off once you overcome the rolling resistance or employing momentum to help propel you.

    Rather then get in a pissing fight over physic and dynamics you're obviously yet to understand, do the research and see how things shake out. There's no free lunch, meaning you're not going to get much out of hydroelectric setup on the butt of a jet. Again it's simple physics, not only will you have to push the water through the jet, but also drag along the resistance on the obstruction (the hydroelectric device) impeding it's free exit. Even if it's in the free flow behind the boat, you still drag this along with you, not to mention the decrease in propulsive power as a result of a jet exit restriction of some sort.

    Ever see a power boat scooting along and look over the stern? You'll note the water flow in the wake seems to dip down, a lot in some cases. This "hole" behind the boat is quite literally the void where the boat just passed and this void, is the equivalent of the mass of the boat. Best of all this void, is physically traveling along with the boat, as it motors along. This is one reason you see us using cute little "rules" like the "cube of it's speed", "proportional to the inverse of it's square root", etc. There's no avoiding the physical realities of mechanical similitude and the other laws of physics. These are the same across all the propulsion choices.

    Simply put, you're not the only one thinking you have found a clever way around, but trust me, most every reasonably way to get a pure electric or hybrid to work has been explored, especially recently, with new technologies coming online. Again, do the research and have a look at the multi million dollar attempts to make large electric craft. They've spent the bucks to sort out the issues and get the most out of these systems, and the recent attempts produced a pretty big boat, covered with solar panels, and though it was as efficient as the custom composite hull and structure could manage, it limped along at 6 - 7 knots for a few hours at a time, then waited for the banks to come up again.
     
  7. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Probably the limited budget part....... or the bit about posting again in a month or two when the plumbing & electrical are complete........ we can discuss it as much as you like or not in the meantime,- get what you will for free both good & bad.
    Best get on with it to be honest,
    you're not being trolled buddy, if you cant stand some minescule resistance here, no way your gunna finish that........

    All the best in your endeavours from Jeff.
     
  8. groper
    Joined: Jun 2011
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    groper Senior Member

    If you had done even the most elementary homework, you would already understand why a car can do 60mph with a fraction of the energy of a similarly sized boat! The fact you have missed it with years of research, is even more worrying!

    Yes of course it works... But you will be closer to 6 kts rather than 10kts, if you are running it further than about 10miles... 10kts will require about 4 times the energy of 6kts... But you already knew that too I suppose? This means your estimates have an accuracy of about +-400%... Considering years of homework, you've clearly got things squared away tight....

    We are only trying to help you... Help you by realising your about to make the biggest financial mistake of your life ... Do you have any idea how many people have blown their life savings on projects like this? If you had been around this forum for a while, you would see the documented evidence of it in black and white...

    The highest funded purpose designed and built projects do succeed in continuously sustaining about 6kts. This is for a +20m catamaran vessel built entirely of carbon fibre. Even the 2m diameter ultra high efficiency props were carbon. A typical 30% propeller energy loss cannot be tolerated on such thin margin feasibility projects... On the other hand, your gonna do it with a transom stern speed boat hull of 40ft with some off the shelf stainless props I suppose? Dreaming is an understatement... You just do not understand the fundamental reasons why despite such huge government and private enterprise funding for green energy projects, they still fail to succeed in a wholistic practical manner. Sure you can make anything move along for some pretty photographs which look great in glossy print, but if they were really useful vessels, why have they not taken off in a big way like the tesla motor car? The reason is simple maths and physics, it's just not feasible YET. Give it another few years, and the economics will begin to make projects like your thinking feasible. It's not that so many talented people don't know how to make it happen, it's just that the most intelligent people realise its foolish to spend money on it in the present...
     
  9. rwatson
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    rwatson Senior Member

    Oh, I don't know Par

    The other hints -

    "I have no boat building or carpentry skills."

    "Within the next month I plan to take a basic boat building carpentry class and another class where I will build a small boat using those skills."

    That and the last posts about power requirements - I don't think you did too badly
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I know Ray, but there's been a touch of sensitivity on the board lately . . . This one has so many red flags, it's hard to be realistic about its outcome as a first build. Granted there are some odds in it's favor, but hell I might hit the lottery some day too.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Oh please, do go into the details, that we may all learn this arcane science ! :D
     
  12. waikikin
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    waikikin Senior Member

    SSSSHHHHH........."plasma drive"

    don't say it too loud.


    Jeff.:eek:
     
  13. NavalSArtichoke
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    NavalSArtichoke Senior Member

    He'd be better off inventing a warp drive and sending that thing into deep space than trying to get it on plane.
     
  14. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    ...

    ??

    ...???

    I get it now. This is to be powered similar to the Underwear Gnomes profit scheme, where
    Underwear + ??? = Profit!!!

    Normally, the two are more or less completed concurrently, as a boat of that size has a number of crews working on it at once, including a crew for the mechanical installations such as engines, running gear etc. The only real requirement is one of practicality and not having two crews trying to work in one space. It's mostly a matter of common sense, as Par says. Don't put something in that will get in the way and stop you from doing something else.

    Powering the boat like you want to is such a radical way that you can't really plan what you are going to have to work around when installing the interior or finishing the exterior. For example, the roof and all the deck will be covered in solar panels, with probably an overhanging framework to expand the capacity for solar panels. So, unless you elevate it all, cleats, stanchions, winches, windows,etc will require some other solution. You might have to figure out some way to continuously orientate them to receive enough "light", but that's your department and you can figure that out. Accommodating the electrical wiring for a huge solar array is nothing similar to what a regular boat needs. The jet drive is a large interior and exterior consideration, and the mysterious drive for that is another.

    In your case, I wouldn't get too involved with anything that was not directly related to your powering scheme, because if it doesn't work you'll probably not want the boat nor will anyone else and so you will not have wasted all the time and money on electrical and plumbing systems that won't be used or would be torn out to be built according to how the new owner wants things. I would concentrate solely on the powering scheme to the point of not finishing the outside or the inside until it had been floated and tested and found satisfactory. The hull should be weighted with waterbags or concrete blocks or something so all trials are done under the final anticipated weight at the correct hull trim.

    Waiting around until technology catches up to your requirements is kind of a waste. If that has to be done, it's an obvious admission that what you want to do won't work.

    By the way, Fulton didn't invent the steamboat, he just challenged the transportation monopoly held on a stretch of river and took others' ideas to make a viable steamboat.

    All the mechanical systems can be easily removed once trials have proven your theory, and then you can invest the considerable time and money it will take to finish the boat.
     

  15. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    If he can get that to work, he would make enough money licensing out the technology that he could get someone else to build the boat - and crew it !
     
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